N2pc than when they simply have to report whether or not a target is present Elimination Certain experimental conditions can eliminate the N2pc entirely. These results have been used to argue for a spatial filtering hypothesis, which proposes that the N2pc reflects the process of ignoring task-irrelevant (i.e., non-target) stimuli. Early investigations of the N2pc critically found that the component was sensitive to the presence of distractors, appearing only when distractors accompanied a target stimulus. Furthermore, N2pc amplitude increases with the number of distractors in the display. The N2pc also disappears when targets in the visual search task are defined as "any oddball object" rather than by one or more specific features. Luck and Hillyard (1994) have argued that in this case, determining whether a given object is a target requires distributing attention over multiple objects in the array (and determining the common features) rather than filtering them. Consequently, the spatial filtering process is discouraged, and the N2pc therefore does not appear. Functional significance The N2pc literature agrees on a few functional characteristics of the N2pc. First, the N2pc appears whenever a person focuses attention on an object. Second, it serves as a direct measure for the direction of focused attention, either to the left or right. Finally, the N2pc is generally believed to be tied to a spatial filtering hypothesis (see above: "Eliminating the N2pc"). The last point regarding the functional significance of the N2pc, however, has been challenged. Some have contested the spatial filtering hypothesis, arguing that the N2pc reflects an enhancement of task-relevant stimulus processing rather than a suppression of irrelevant stimuli. Other work has explored further cognitive processes that could be linked to the N2pc. For instance, the classic visual search paradigm that elicits the N2pc could be broken down further into processes of shifting attention, and spatially based processing of non-target locations. When combining the visual search task with visual cues that drew attention to spatial locations in the display, experimenters found that while the N2pc may not reflect shifts of attention, it may still reflect processing of a location in space that may or may not contain a target. See also Bereitschaftspotential C1 and P1 Contingent negative variation Difference due to memory Early left anterior negativity Error-related negativity Late positive component Lateralized readiness potential Mismatch negativity N100 N170 N400 P3a P3b P200 P300 (neuroscience) P600 Somatosensory evoked potential Visual N1 References Electroencephalography Evoked potentials